$\sum\limits_{j=1}^{2 }{{(5j)}}=$
Answer: What is the question asking for? $\sum$ tells us to find the sum. The question is asking for the sum of the values of $5j$ from $j = 1$ to $j = 2$. Evaluating $\begin{aligned} \sum\limits_{j=1}^{2 }{({5j})}&= (5(1)) + (5(2)) \\\\ &= 5 + 10 \\\\ &= 15\end{aligned}$ The answer $\sum\limits_{j=1}^{2 }{({5j})}=15$